Electric machine

ABSTRACT

An electric machine having a stator assembly that includes a stator core and a coil supported by the stator core and a rotor assembly that includes a shaft and a rotor supported by the shaft that is in magnetic interaction with the stator core. The electric machine may include a single sensor configured to detect magnetic polarities of the rotor as the rotor rotates relative to the sensor and to generate a signal representing the detected magnetic polarities of the rotor. The signal and an inverted version of the signal are utilized to control current through the coil. The current may be controlled indirectly by controlling the application of voltage to the coil. The sensor may be encapsulated on a circuit board to positively position the sensor relative to the circuit board. The circuit board may be mounted to a bearing housing of the electric machine. The sensor may be received in a pocket of a bearing housing of the electric machine so the sensor is positively positioned relative to the rotor. The rotor may be connected to the shaft with an encapsulation material. The rotor may be formed as a single cylinder of ferrite. A tapered air gap may be formed between a portion of the stator core and a corresponding portion of the rotor. The electric machine may be a C-frame electric motor with the I-bar portion formed of grain-oriented electric steel.

BACKGROUND OF THE INVENTION

The invention relates to electric machines, and more particularly toelectrically commutated C-frame electric motors.

C-frame electric motors are used in a wide range of applicationsincluding, among others, bathroom and kitchen ventilation fans,microwave oven fans, convection oven fans, furnaces, refrigerators,evaporative cooler fans, dishwashers, humidifiers, portable medicalequipment, pumps, condenser fans, and the like. Improvements to C-frameelectric motors that enhance performance and reduce costs would bewelcomed by those in the art.

SUMMARY OF THE INVENTION

In one construction, the invention provides an electric machine having astator assembly, a rotor assembly, and a single sensor. The statorassembly includes a stator core and a coil supported by the stator core.The rotor assembly includes a shaft and a rotor supported by the shaftfor rotation with the shaft relative to the stator core. The rotorincludes first and second magnetic poles and is in magnetic interactionwith the stator core. The single sensor is configured to detect magneticpolarities of the rotor as the rotor rotates relative to the sensor andto generate a signal representing the detected magnetic polarities ofthe rotor. The signal is in a first state when the first magnetic poleis detected and a second state when the second magnetic pole isdetected. The signal is inverted to form an inverted signal. The signalis utilized to control current through the coil in a first directionwhen the signal is in the first state and the inverted signal isutilized to control current through the coil in a second direction whenthe signal is in the second state. The current through the coil resultsin an alternating magnetic field in the stator core. In someconstructions, the current is controlled indirectly (e.g., bycontrolling the voltage applied to the coil which produces the currentthrough the coil).

In another construction, the invention provides an electric machinehaving a stator assembly, a rotor assembly, and a control circuit. Thestator assembly includes a stator core and a coil assembly supported bythe stator core. The stator core defines a rotor opening and the coilassembly includes a bobbin and a coil wound on the bobbin. The rotorassembly includes a shaft and a permanent magnet rotor supported by theshaft. The rotor rotates with the shaft relative to the stator core,includes first and second magnetic poles, is at least partiallypositioned in the rotor opening, and is in magnetic interaction with thestator core. The control circuit is configured to receive power from apower supply and control a current through the coil. The current createsan alternating magnetic field in the stator core. The control circuitincludes a single Hall device, an inverter, and a switching circuit. TheHall device detects magnetic polarities of the rotor as the rotorrotates relative to the Hall device and generates a signalrepresentative of the detected magnetic polarities of the rotor. Thesignal is in a first state when the first magnetic pole is detected anda second state when the second magnetic pole is detected. The switchingcircuit is connected to the coil. The signal is utilized to controloperation of the switching circuit to allow the current through the coilin a first direction when the signal is in the first state. The invertedsignal is utilized to allow the current through the coil in a seconddirection when the signal is in the second state.

In another construction, the invention provides an electric machinehaving a stator assembly, a rotor assembly, first and second bearinghousings, a circuit board, and first and second fasteners. The statorassembly includes a stator core and a coil supported by the stator core.The stator core defines a first bore. The rotor assembly includes ashaft, a rotor supported by the shaft for rotation with the shaftrelative to the stator core, and first and second bearings secured tothe shaft on opposite sides of the rotor. The first bearing housingreceives the first bearing and defines a second bore which aligns withthe first bore. The second bearing housing receives the second bearingand defines a third bore which aligns with the first and second bores.The first fastener is received in the second, first, and third bores tosecure the first and second bearing housings to the stator assembly. Thesecond fastener is spaced from the first fastener and secures thecircuit board to the second bearing housing.

In another construction, the invention provides an electric machinehaving a stator assembly and a rotor assembly. The stator assemblyincludes a stator core and a coil supported by the stator core. Thestator core includes a C-frame portion that defines a rotor opening andan I-bar portion that is formed of grain-oriented electric steel. Therotor assembly includes a shaft and a rotor supported by the shaft forrotation with the shaft relative to the stator core.

In another construction, the invention provides an electric machinehaving a stator assembly and a rotor assembly. The stator assemblyincludes a stator core and a coil assembly supported by the stator core.The stator core defines a rotor opening and the coil assembly includes abobbin and a coil wound on the bobbin. The rotor assembly includes ashaft and a one-piece permanent magnet rotor supported by the shaft. Therotor rotates with the shaft relative to the stator core, includes firstand second magnetic poles, is at least partially positioned in the rotoropening, and is in magnetic interaction with the stator core. At least aportion of the rotor and at least a portion of the shaft areencapsulated in a material that connects the rotor to the shaft.

In yet another construction, the invention provides an electric machinehaving a stator assembly, a rotor assembly, a sensor, and first andsecond bearing housings. The stator assembly includes a stator core anda coil assembly supported by the stator core. The stator core defines arotor opening and the coil assembly includes a bobbin and a coil woundon the bobbin. The rotor assembly includes a shaft, a rotor supported bythe shaft, and first and second bearings secured to the shaft onopposite sides of the rotor. The rotor rotates with the shaft relativeto the stator core, includes at least first and second magnetic poles,is at least partially positioned in the rotor opening, and is inmagnetic interaction with the stator core. The sensor is configured todetect magnetic polarities of the rotor and to generate a signalrepresenting the detected magnetic polarities of the rotor. The signalis utilized to control a current through the coil. The first bearinghousing receives the first bearing and the second bearing housingreceives the second bearing. The second bearing housing defines a pocketthat receives a portion of the sensor to locate the sensor relative tothe rotor.

Further aspects of the invention, together with the organization andmanner of operation thereof, will become apparent from the followingdetailed description of the invention when taken in conjunction with theaccompanying drawings wherein like elements have like numeralsthroughout the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further described with reference to the accompanyingdrawings, which show constructions of the invention. However, it shouldbe noted that the invention as disclosed in the accompanying drawings isillustrated by way of example only. The various elements andcombinations of elements described below and illustrated in the drawingscan be arranged and organized differently to result in constructionswhich are still within the spirit and scope of the invention. Also, itis understood that the phraseology and terminology used herein is forthe purpose of description and should not be regarded as limiting. Theuse of “including,” “comprising,” or “having” and variations thereofherein is meant to encompass the items listed thereafter and equivalentsthereof as well as additional items. Unless specified or limitedotherwise, the terms “mounted,” “connected,” “supported,” and “coupled”are used broadly and encompass both direct and indirect mountings,connections, supports, and couplings. Further, “connected” and “coupled”are not restricted to physical or mechanical connections or couplings.

FIG. 1 is a perspective view of a first C-frame electric motorincorporating aspects of the invention.

FIG. 2 is a perspective view of the C-frame electric motor of FIG. 1.

FIG. 3 is a partial exploded view of the C-frame electric motor of FIG.1.

FIG. 4 is a top view of the C-frame electric motor of FIG. 1.

FIG. 5 is a side view of the C-frame electric motor of FIG. 1.

FIG. 6 is a rear view of the C-frame electric motor of FIG. 1.

FIG. 7 is a perspective view of a second C-frame electric motorincorporating aspects of the invention.

FIG. 8 is a rear view of the C-frame electric motor of FIG. 7.

FIG. 9 is a side view of the C-frame electric motor of FIG. 7.

FIG. 10 is a partial exploded view of the C-frame electric motor of FIG.7.

FIG. 11 is a sectional view of a rotor assembly of the C-frame electricmotors shown in FIGS. 1 and 7.

FIG. 12 is a sectional view of an alternative rotor assembly for theC-frame electric motors shown in FIGS. 1 and 7.

FIG. 13 schematically illustrates a functional diagram of a controlcircuit of the C-frame electric motors shown in FIGS. 1 and 7.

FIG. 14 is a lamination of a stator core of the C-frame electric motorsshown in FIGS. 1 and 7.

FIG. 15 is an alternative lamination for use in the stator core of theC-frame electric motors shown in FIGS. I and 7.

FIG. 16 schematically illustrates the magnetic interaction between apermanent magnet rotor and a stator core formed of the laminations ofFIG. 15.

FIG. 17 is a sectional view of a bearing housing of the C-frame electricmotor shown in FIG. 1.

FIG. 18 is a sectional view of a bearing housing of the C-frame electricmotor shown in FIG. 7.

FIG. 19 is a sectional view of an alternative bearing housing for theC-frame electric motors shown in FIGS. 1 and 7.

DETAILED DESCRIPTION

A first construction of an electric motor 10 is illustrated in FIGS.1-6. A second construction of an electric motor 100 is illustrated inFIGS. 7-10. Each motor 10, 100 is a direct current (“DC”), brushlesspermanent magnet (“BLPM”), C-frame, electric motor. Similar componentsof the motors 10 and 100 are indicated using like reference numerals inthe drawings. It should be understood that aspects of the invention maybe utilized in other types of electric machines and the motors 10 and100 are merely shown and described as two such examples.

With reference to FIG. 3, the motor 10 includes a stator assembly 14, arotor assembly 18 (FIG. 11), a first bearing housing 22, a secondbearing housing 26, a circuit board 30, first fasteners 31, and secondfasteners 32. With reference to FIG. 10, the motor 100 is similar to themotor 10 except it instead includes a second bearing housing 27, anencapsulated circuit board 35, and first fasteners 33.

Referring to FIGS. 3 and 10, the stator assembly 14 includes a laminatedcore (i.e., stator core) and a coil assembly. The laminated coreincludes a C-frame portion 40 and an I-bar portion 44. The C-frameportion 40 defines a window or rotor opening 48 for receiving the rotorassembly 18 (FIG. 11). The C-frame portion 40 also defines bores 50 forreceiving the first fasteners 31, 33. The illustrated bores 50 arethrough bores. The C-frame portion 40 and the I-bar portion 44 are eachmade of a plurality of laminations 52 (FIG. 14). The laminations 52 areheld together using suitable means such as welding, adhesive bonding,mechanical fasteners (e.g., rivets), and the like. The size and power ofthe motor 10 are determined in part by the number of laminations 52. Theillustrated laminations 52 are standard shaded pole motor laminationswith the window 48 defining shaded pole recesses. In the illustratedconstructions, the motor 10, 100 utilizes fewer of the laminations 52than a shaded pole motor having similar performance specifications. Inother constructions, the window 48 in the C-frame portion 40 isalternative shaped. For example, the window may form a tapered air gapbetween at least a portion of the laminated core and the rotor assembly18. A lamination 56 having a window forming such a tapered air gap isshown in FIG. 15. In some constructions, a tapered air gap providesenhanced performance of the motor 10, 100. A tapered air gap may causethe rotor to park relative to the stator core in a consistent position,which may enhance the starting capability of the motor 10, 100. Theshape of the tapered air-gap influences the back electromotive force(BEMF) waveform and therefore the electric current waveform and therunning performance of the motor. A sensor (e.g., the sensor 216discussed below) can be placed in any position adjacent to the taperedair gap, the position being selected to allow the improvement of motorperformance (e.g., by phase advancement).

The C-frame and I-bar portions 40 and 44 of the laminations 52 areformed of non-grain-oriented electric steel, which is commonly employedfor the manufacturing of rotating electrical machines. In someconstructions, the I-bar portion 44 is formed using grain-orientedelectric steel. With reference to FIG. 16, the magnetic flux lines inthe I-bar portion 44 are substantially parallel to the longer edges ofthe I-bar portion 44. It is therefore advantageous to manufacture theI-bar 44 by stacking laminations of grain-oriented electric steel. Inone construction, the I-bar portion 44 is oriented with the length alongthe preferred magnetization (or “easy” rolling) direction of theelectric steel, i.e., the horizontal direction in FIG. 16. Suchorientation reduces iron losses and increases magnetic permeance of thestator core. With continued reference to FIG. 16, the magnetic fluxlines in the C-frame portion 40 have a different specific pattern.Accordingly, the C-frame portion 40 is formed using non-grain-orientedelectric steel. The coil 64 is schematically illustrated in FIG. 16.

The coil assembly includes a bobbin 60 and a coil 64 of wire wrappedaround the bobbin 60. As illustrated in FIG. 1, the I-bar portion 44extends through the center of the bobbin 60 to support the coil assemblyon the laminated core. The bobbin 60 includes two terminal assemblies66. End portions of the coil 64 are electrically connected to thecircuit board 30 via the terminal assemblies 66. In the illustratedconstruction, the bobbin 60 is formed of a plastic material. In otherconstructions, the bobbin 60 is alternatively shaped and/or formed.

With reference to FIG. 11, the rotor assembly 18 includes a shaft 68, arotor 72 supported by the shaft for rotation with the shaft 68 relativeto the stator assembly 14, and bearings 76 secured to the shaft 68 onopposite sides of the rotor 72. The bearings 76 are schematicallyillustrated. The illustrated rotor 72 is a permanent magnet rotor thatis formed as a solid ferrite cylinder having a first magnetic pole(e.g., a north magnetic pole) and a second magnetic pole (e.g., a southmagnetic pole). The rotor 72 includes an axial bore 80 having an innerdiameter that is larger than the outer diameter of the shaft 68. Forassembly, the bore 80 of the rotor 72 is radially centered on the shaft68, and the rotor 72 and a portion of the shaft 68 are encapsulated in asuitable encapsulation material 81 (e.g., a plastic material, anelastomeric material, a resin material, and the like). The encapsulationmaterial 81 is between the rotor 72 and the shaft 68 and on the outersurfaces of the rotor 72. The encapsulation material 81 connects therotor 72 to the shaft 68 without the use of adhesives (e.g., glue) orother fastening means which are typically utilized for such purposes,thus potentially simplifying the manufacturing process. Theencapsulation material 81 also protects the rotor 72 from chipping,especially when the rotor 72 is formed of a brittle material such asferrite. The shaft 68 extends axially from the rotor 72 and is supportedon each end by the bearings 76. The bearings 76 are supported byrespective bearing housings 22 and 26, 27. In other constructions, therotor 72 is alternatively connected to the shaft 68 with theencapsulation material 81. A rotor assembly 19 is illustrated in FIG. 12as an exemplary construction. The rotor assembly 19 is similar to therotor assembly 18 except it instead includes a rotor 73. The rotor 73includes an axial bore 82 having an inner diameter that is substantiallyequal to the outer diameter of the shaft 68. Accordingly, theencapsulation material 81 is not between the rotor 73 and the shaft 68.Instead, encapsulation material 81 on the axial ends of the rotor 73connects the rotor 73 to the shaft 68.

With reference to FIGS. 3 and 10, the first bearing housing 22 includesa main body 22 a and arm portions 22 b that extend from the main body 22a. The main body 22 a is sized to receive a respective bearing 76 (FIG.11) and a portion of the rotor 72. As illustrated in FIG. 1, the shaft68 extends through the main body 22 a for connection to a load.Referring to FIGS. 3 and 10, each arm portion 22 b defines a bore 22 cfor receiving a respective first fastener 31, 33. The illustrated bores22 c are through bores which align with the bores 50 in the C-frameportion 40.

With reference to FIGS. 3 and 17, the second bearing housing 26 alsoincludes a main body 26 a and arm portions 26 b that extend from themain body 26 a. In addition to being sized to receive a respectivebearing 76 (FIG. 11) and a portion of the rotor 72, the main body 26 ais also sized to receive an end portion of the shaft 68. The main body26 a defines alignment holes or sensor pockets 26 d (FIGS. 2 and 3).Each arm portion 26 b defines a bore 26 e for receiving an end portionof a respective first fastener 31 and a projection 26 f for receiving arespective second fastener 32. The illustrated bores 26 e are blindbores that align with the bores 50 in the C-frame portion and the bores22 c of the first bearing housing 22. The illustrated projections 26 fare integrally cast pins that are axially aligned with the bore 26 e. Inother constructions, the projections 26 f are alternatively formed(e.g., threaded studs) and/or alternatively positioned on the secondbearing housing 26.

With reference to FIGS. 10 and 18, the second bearing housing 27 issimilar to the second bearing housing 26 (FIG. 3) except the secondbearing housing 27 does not include projections similar to theprojections 26 f (FIG. 3). Further, the second bearing housing 27includes through bores 27g instead of the blind bores 26 e (FIG. 3). Inother constructions, the second bearing housing 26, 27 is alternativelyshaped and/or formed. In one exemplary alternative construction, asecond bearing housing 28, shown in FIG. 19, is similar to the secondbearing housing 26 (FIG. 3) except the second bearing housing 28 doesnot include projections similar to the projections 26 f (FIG. 3) and thearm portions 28 b each also define a bore 28 h for receiving a fastener(e.g., a threaded fastener). The illustrated bores 28 h are blind boreswhich are axially aligned with the bores 28 e. The bores 28 h can bealternatively positioned in other constructions.

Referring again to FIG. 3, the circuit board 30 supports a controlcircuit 200 (FIGS. 13) that is configured to receive power from asuitable power supply (e.g., a 120 volt, 60 Hz alternating current powersupply) and control a current through the coil 64. In the illustratedconstructions, and as described herein, controlling current through thecoil 64 includes controlling a voltage applied to the coil 64. Thevoltage produces a current through the coil 64. The current establishesan armature reaction magnetic field in the air-gap that separates thelaminated core and the rotor 72. The armature reaction field interactswith the permanent magnet rotor magnetization to produce a rotationaltorque and cause rotor movement. The values of the applied voltage andof the back electromotive force (BEMF) influence the values of thecurrent through the coil 64, the armature field, and the torque producedat the shaft 68. In other constructions, the current may bealternatively controlled.

With reference to FIG. 2, the circuit board 30 includes terminals 90that are electrically connectable to a power supply. However, thecircuit board 30 can be connected to a power supply by other means.Referring back to FIG. 3, the circuit board 30 defines bores 30 a forconnection of the circuit board 30 to the second bearing housing 26, 27,28. The illustrated bores 30 a are through bores. In some constructions,the bores 30 a align with the projections 26 f of the second bearinghousing 26. In other constructions, the bores 30 a align with the bores27 g of the second bearing housing 27. In yet other constructions, thebores 30 a align with the bores 28 h of the second bearing housing 28.

The circuit board 30 also defines sets of sensor bores 30 b and abearing housing opening 30 c. With reference to FIGS. 2, 3, 6-8, and 10,each illustrated set of sensor bores 30 b aligns with a correspondingsensor pockets 26 d, 27 d, 28 d in the second bearing housing 26, 27,28, respectively. With continued reference to FIGS. 2, 3, 6-8, and 10,the illustrated bearing housing opening 30 c is sized to receive aportion of the second bearing housing 26, 27, 28.

With reference to FIG. 10, the encapsulated circuit board 35 includesthe circuit board 30 covered by a layer of encapsulation material 83(e.g., a plastic material, an elastomeric material, a resin material,and the like). In one construction, the circuit board 30 is encapsulatedusing a co-molding (injection) process to form the encapsulated circuitboard 35. In other constructions, the circuit board 30 may bealternatively encapsulated to form the circuit board 35. Theencapsulation material 83 protects the circuit board 30 fromenvironmental conditions (e.g., humidity) and vibration.

For assembly of the motor 10, the rotor assembly 18 is inserted in thewindow 48 and the first and second bearing housings 22 and 26 arepositioned on opposite sides of the stator assembly 14 to receive arespective bearing 76. The first fasteners 31 are received in the bores22 c in the first bearing housing 22, the bores 50 in the C-frameportion 40, and the bores 26 e in the second bearing housing 26. Theillustrated first fasteners 31 are self-tapping screws that are tappedinto the bores 26 e to secure the first and second bearing housings 22and 26 to the stator assembly 14. The rotor 72 is positioned formagnetic interaction with the stator assembly 18 when the motor 10 isassembled. In the illustrated construction, the rotor 72 extends axiallybeyond the stator core in each direction. The circuit board 30 ispositioned adjacent the second bearing housing 26 so a portion of thesecond bearing housing 26 extends through the bearing housing opening 30c and a portion of the projections 26 f extend through the bores 30 a.The second fasteners 32 (e.g., push nuts) are connected to the portionsof the projections 26 f extending through the bores 30 a to fixedlysecure the circuit board 30 to the second bearing housing 26. Terminalson the circuit board 30 are positioned in the terminal assemblies 66 toelectrically connected the circuit board 30 to the coil 64. Receipt ofthe circuit board terminals in the terminal assemblies 66 providesadditional support to the circuit board 30.

The motor 100 is assembled similarly to the motor 10 except the firstfasteners 33 also extend through the bores 27 g of the second bearinghousings 27 and the bores 30 a of the circuit board 30. The firstfasteners 33 are similar to the first fasteners 31 except the firstfasteners 33 include a longer length than the first fasteners 31 thusallowing receipt of the first fasteners 33 in the bores 30 a. The endportions of the first fasteners 33 that extend through the bores 30 aare releasably secured by the second fasteners 32 (e.g., push nuts) toconnect the circuit board 30 to the second bearing housing 27.

In other constructions, the circuit board 30 is connected to the secondbearing housing 28. A motor including the second bearing housing 28would include an assembly similar to the motor 10 except fastenersreceived in the bores 28 h in the second bearing housing 28 would extendthrough the bores 30 a instead of the projections 26 f. In one exemplaryconstruction, the fasteners received in the bores 28 h are threadedstuds to which fasteners (e.g., the second fasteners 32) are secured toconnect the circuit board 30 to the second bearing housing 28. Inanother exemplary construction, the fasteners received in the bores 28 hinclude a head positioned adjacent the circuit board 30 so the fastenersreceived in the bores 28 h solely connect the circuit board 30 to thesecond bearing housing 28. Connection of the circuit board 30 to thesecond bearing housing 26, 28 without using the fasteners that securethe stator assembly, the rotor assembly, and the bearing housingstogether (e.g., the first fasteners 31) allows for replacement of thecircuit board 30 and/or connection of the motor 10, 100 to a loadwithout disturbing the factory established alignment between the statorand rotor assemblies 14 and 18.

The control circuit 200 is schematically illustrated in FIG. 13. Thecontrol circuit 200 includes a first voltage regulator 204, a secondvoltage regulator 208, a single sensor 216, a buffer 220, a first delay224, an inverter 228, a second delay 232, a first AND gate 236, a secondAND gate 240, a switching circuit 244, a current sensor 248, and acondition monitoring circuit 252.

The first voltage regulator 204 utilizes power received from a powersupply 212 (e.g., a 120 volt, 60 Hz alternating current power supply) togenerate an upper rail direct current voltage DC1 and a ground GND. Inone construction, the first voltage regulator 204 includes acapacitor-divider type voltage regulator with a zener diode that limitsthe upper rail direct current voltage DC1 by dissipating any extraenergy as heat, thus eliminating the tendency of excess power input toincrease the upper rail direct current voltage DC1. In the illustratedconstruction, the first voltage regulator 204 receives a power inputfrom the power supply 212 via the terminals 90 (FIGS. 2 and 7).

The second voltage regulator 208 utilizes the upper rail direct currentvoltage DC1 to generate a lower rail direct current voltage DC2. Thelower rail direct current voltage DC2 is utilized to power the sensor216, the buffer 220, the first and second delays 224 and 232, theinverter 228, the first and second AND gates 236 and 240, and thecondition monitoring circuit 252. In one construction, the secondvoltage regulator 208 is a linear voltage regulator. In otherconstructions, other types of power supplies (e.g., voltage regulators)may be utilized to provide power to the components of the controlcircuit 200.

The single sensor 216 (e.g., a Hall device) is selectively mounted inone of the sets of sensor bores 30 b on the circuit board 30 so thesensor 216 extends from the circuit board 30 and is received adjacent aradial portion of the rotor 72 in the corresponding sensor pocket 26 d,27 d, 28 d of the second bearing housing 26, 27, 28. In the illustratedconstruction, a portion of the sensor 216 most outward from the circuitboard 30 is positioned to contact an outer surface of the outermostlamination 52 of the stator core directly adjacent the window 48. Suchplacement maximizes the magnetic interaction between the rotor 72 andthe sensor 216 without eliminating stator core material. The mounting ofthe sensor 216 may be selected based on the desired direction ofrotation of the rotor 72 (e.g., clockwise, counter-clockwise). Placementof the sensor 216 in the sensor pocket 26 d, 27 d, 28 d ensures properalignment of the sensor 216 relative to the rotor 72, seals the rotorcavity, and protects the sensor from environmental conditions. For theencapsulated circuit board 35, the sensor 216 is connected to thecircuit board 30 and positioned in a fixture to positively define aposition of the sensor 216 relative to the circuit board 30. The circuitboard 30 is then encapsulated in the encapsulation material 83, whichmaintains the position of the sensor 216 relative to the circuit board30. The encapsulated sensor 217 (FIGS. 7-10) is then received in thecorresponding sensor pocket 26 d, 27 d, 28 d. In the illustratedconstruction, the outer diameter of the encapsulated sensor 217 issubstantially equal to the inner diameter of the sensor pocket 26 d, 27d, 28 d.

The sensor 216 is configured to detect magnetic polarities of the rotor72 as the rotor 72 rotates relative to the sensor 216. The sensor 216generates a signal S representative of the detected magnetic polaritiesof the rotor 72. In the illustrated construction, the signal S is in afirst state when the north magnetic pole of the rotor 72 is detected anda second state when the south magnetic pole of the rotor 72 is detected.

In one construction, the sensor 216 is a latching Hall effect sensor(e.g., model number HAL505UA-E provided by Micronas Intermetall ofFreiburg, Germany). The sensor 216 generates a signal S which turns high(e.g., the first state) when a north magnetic pole of the rotor 72 isdetected and turns low (e.g., the second state) when a south magneticpole of the rotor 72 is detected. The signal S does not change if themagnetic field is removed. Instead, the opposite magnetic field polarityis detected to change the state of the signal S. In other constructions,other types of sensors having other types of outputs are utilized.

The buffer 220 receives an input representative of the signal S andgenerates a buffered signal BS that is isolated from the signal S. Inone construction, the buffer 220 is an inverter. In other constructions,other types of buffers may be utilized.

The first delay 224 receives an input representative of the bufferedsignal BS and generates a first control signal C1. In one construction,the first delay 224 is a resistive-capacitance delay. The duration ofthe first delay 224 may be changed by changing the values of thecomponents of the first delay 224.

The first AND gate 236 receives an input representative of the firstcontrol signal C1 and generates a second control signal C2. The secondcontrol signal C2 is identical to the first control signal C1 unless anoverride condition exists (as discussed below).

The inverter 228 also receives an input representative of the bufferedsignal BS and generates an inverted buffered signal IBS. In theillustrated construction, the inverted buffered signal EBS is logic highwhen the signal S is logic low and logic low when the signal S is logichigh.

The second delay 232 receives an input representative of the invertedbuffered signal IBS and generates a third control signal C3. The seconddelay 232 includes a construction similar to the first delay 224. Inother constructions, other delay circuitry is utilized.

The second AND gate 240 receives an input representative of the thirdcontrol signal C3 and generates a fourth control signal C4. The fourthcontrol signal C4 is identical to the third control signal C3 unless anoverride condition exists (as discussed below).

The switching circuit 244 (e.g., an H-bridge circuit) is connected tothe coil 64 via the terminal assemblies 66 (FIGS. 1 and 9). Theswitching circuit 244 allows current I1 through the coil 264 in a firstdirection when the signal S from the sensor 216 is in the first stateand current I2 through the coil 264 in a second direction when thesignal S from the sensor 216 is in the second state. The switchingcircuit 244 limits the current I1, I2 through the coil 64 when anoverride condition exists, regardless of the state of the signal S.

The illustrated switching circuit 244 includes first and second pairs ofswitching elements. The first pair of switching elements is formed ofswitching elements T1 and T4 and the second pair of switching elementsis formed of switching elements T2 and T3. Switching elements T1 and T2represent the high-side switching elements of the pairs and each receivethe upper rail direct current voltage DC1. In one construction, theswitching elements T1 and T2 are darlington transistors which providecurrent gain. The switching elements T3 and T4 represent the low-sideswitching elements of the pairs are each connected to the common rail ofthe switching circuit 244. The common rail is connected to ground GNDthrough the current sensor 248. In one construction, the switchingelements T3 and T4 are MOSFETS.

Each switching element T1, T2, T3, and T4 includes a conducting stateand a non-conducting state. The state of the switching element T1 iscontrolled by the first control signal C1. In one construction, thefirst control signal C1 controls the state of the switching element T1via a switch (e.g., a MOSFET). The state of the switching element T2 iscontrolled by the third control signal C3. In one construction, thethird control signal C3 controls the state of the switching element T2via a switch (e.g., a MOSFET). The state of the switching element T3 iscontrolled by the fourth control signal C4. The state of the switchingelement T4 is controlled by the second control signal C2. Accordingly,the first pair of switching elements is in a conducting state when bothswitching elements T1 and T3 are in a conducting state, and the firstpair of switching elements is in a non-conducting state when at leastone of the switching elements T1 and T3 is in a non-conducting state.Similarly, the second pair of switching elements is in a conductingstate when both switching elements T2 and T3 are in a conducting state,and the second pair of switching elements is in a non-conducting statewhen at least one of the switching elements T2 and T3 is in anon-conducting state. The first and second delays 224 and 232 areutilized to ensure the first and second pairs of switching elements arenot simultaneously in a conducting state. Simultaneous conductance ofboth pairs of switching elements may adversely effect the operation ofthe sensor 216, as well as shorting the upper rail direct currentvoltage DC1 to ground GND resulting in excessive power dissipation.Therefore, the second pair of switching elements is in a non-conductingstate when the first pair of switching elements is in a conducting stateand the first pair of switching elements is in a non-conducting statewhen the second pair of switching elements is in a conducting state. Inother constructions, other types of switching circuits are utilized.

The current sensor 248 receives an input representative of the currentI1, I2 through the coil 64 and generates a current signal VIrepresentative of the current I1, I2 through the coil 64. In oneconstruction, the current sensor 248 includes a resistor connectedbetween the common rail of the switching circuit 244 and ground GND.

The condition monitoring circuit 252 includes a voltage detectioncircuit 256, a current limit circuit 260, and an override circuit 264.The voltage detection circuit 256 receives an input representative ofthe upper rail direct current voltage DC1 and generates a monitoredvoltage signal MV. The current limit circuit 260 receives an inputrepresentative of the current signal VI and generates a monitoredcurrent signal MC. The override circuit 264 receives an inputrepresentative of the monitored voltage signal MV and an inputrepresentative of the monitored current signal MC and generates anoverride condition signal L. The override condition signal L is in afirst state (e.g., logic low) when an override condition exists and asecond state (e.g., logic high) when an override condition does notexist. When in the first state, the override condition signal L limitsthe current I1, I2 through the coil 64 (i.e., an override conditionexists). When in the second state, the override condition signal Lallows the current I1, I2 through the coil 64 (i.e., an overridecondition does not exist).

In the illustrated construction, an override condition exists when theupper rail direct current voltage DC1 is below a predetermined value(e.g., below 80% of the expected upper rail direct current voltage DC1)and/or when the current signal VI is above a predetermined range (e.g.,above 200 mA). In other constructions, the thresholds are alternativelyestablished. If the upper rail direct current voltage DC1 is below apredetermined value, the switching circuit 244 may not operate properly.Similarly, if the monitored current signal is above a predeterminedvalue, the current I1, I2 through the coil 64 may be exceedingacceptable limits (e.g., a locked rotor condition) or the efficiency ofthe motor 10, 100 may be being reduced.

The first and second AND gates 236 and 240 receive an inputrepresentative of the override condition signal L. If an overridecondition exists, the override condition signal L is utilized to changethe second and fourth control signal C2 and C4 so the second controlsignal C2 is different than the first control signal C1 and the fourthcontrol signal C4 is different than the third control signal C3. Whenthe first and second control signals C1 and C2 are different, theswitching circuit 244 limits the current I1 through the coil 64 in thefirst direction. When the third and fourth control signals C3 and C4 aredifferent, the switching circuit 244 limits the current I2 through thecoil 64 in the second direction. The switching circuit 244 limitscurrent through the coil 64 by stopping the application of the upperrail direct current voltage DC1 to the coil 64. Current may continue toflow through portions of the switching circuit 244 after application ofthe upper rail direct current voltage DC1 is stopped.

In one construction, the condition monitoring circuit 252 includes atransistor-ORed circuit. The voltage detection circuit 256 includes atransistor that is turned ON when the upper rail direct current voltageDC1 is below a predetermined level and turned OFF when the upper raildirect current voltage DC1 is above the predetermined level. When thetransistor is turned ON, the generated override signal L is in the firststate (i.e., an override condition exists). When the transistor isturned OFF, the generated override signal L may be in the second state(i.e., an override condition does not exist). The current limit circuit260 includes a transistor that turns ON when the current signal VI isabove a predetermined value and turned OFF when the current signal VI isbelow the predetermined value. When the transistor is turned ON, thegenerated override signal L is in the first state (i.e., an overridecondition exists). When the transistor is turned OFF, the generatedoverride signal L may be in the second state (i.e., an overridecondition does not exist). In the illustrated construction, the overridesignal L is in the second state when the transistors of each of thevoltage detection circuit 256 and the current limit circuit 260 areturned OFF. In one construction, the override circuit 264 includes abuffer to buffer the voltage detection circuit 256 and the current limitcircuit 260 from the switching circuit 244 and the upper rail directcurrent voltage DC1.

The illustrated control circuit 200 utilizes the condition monitoringcircuit 252 and the delay circuits 224 and 232 to increase theefficiency of the motor 10, 100. The switching circuit 244 changes thedirection of the current I1, I2 through the coil 64 to generate analternating magnetic field in the laminated core. The magnetic fieldinteracts with the permanent magnet rotor magnetization to produce arotational torque and cause the rotor 72 to rotate with the shaft 68relative to the laminated core. Continuous establishment of the currentI1, I2 through the coil 64 is not necessary to cause the rotor 72 torotate properly. Further, establishment of the current I1, I2 throughthe coil 64 may generate little or no torque output at the shaft 68 whenthe back electromotive force (BEMF) is low. Accordingly, suchestablishment of the current I1, I2 through the coil 64 results inreduced efficiency of the motor 10, 100. The illustrated motor 10, 100includes at least two periods of limited current through the coil 64 foreach revolution of the rotor 72. These periods reduce the amount ofpower input necessary to run the motor 10, 100. Accordingly, theefficiency of the motor 10, 100 is increased.

In the illustrated constructions, the periods of limited current throughthe coil 64 include periods of limited current through the coil 64before and after the switching of the current I1, I2 in the coil 64 bythe switching circuit 244. The periods of limited current through thecoil 64 before switching of the current are established by setting thepredetermined level of the current limit circuit to represent a value ofcurrent I1, I2 through the coil 64 just above an efficient limit (e.g.,a value on the current curve where the back electromotive force (BEMF)is insufficient to generate a predetermined amount of torque output).When the current I1, I2 exceeds the efficient limit (e.g., 200 mA),additional application of power to the coil 64 results in wasted energy.Accordingly, the current limit circuit causes the condition monitoringcircuit 252 to generate a logic low override condition signal L (i.e.,an override condition exists). The switching circuit 244 thus limitscurrent I1, I2 through the coil 64. The periods of limited currentthrough the coil 64 after switching of the current are established bysetting the delay duration of the delay circuits 224 and 232. The delaycircuits 224 and 232 delay the application of the upper rail directcurrent voltage DC1 to the coil 64, and thus the establishment ofcurrent I1, I2 through the coil 64, after the switching of the currentI1, I2 by the switching circuit 244. In the illustrated construction,the periods of no current through the coil 64 represent approximatelyfour degrees of a full rotation of the rotor. The periods of no currentthrough the coil 64 may be longer or shorter in other constructions.

In the illustrated constructions, the speed of the motor 10, 100 ispre-set and adjustable by changing the values of the components of thecontrol circuit 200.

The specific motor constructions shown are for exemplary purposes.Aspects of the invention described herein may be used in other types ofelectric motors. Although the control circuit 200 is shown and describedherein as having specific solid state electronic devices such asMOSFETS, resistors, transistors, AND gates, inverters, etc., it is to beunderstood that a wide variety of circuit elements could be chosen bythose skilled in the art in order to achieve the advantages of theinvention. In addition, those skilled in the art will recognize thatsome elements could be removed, added, or substituted with otherelements. In some constructions, portions of the control circuit 200 canbe implemented using a programmable device (e.g., a microprocessor, amicrocontroller, a digital signal processor, etc.) that utilizessoftware stored in a memory.

The constructions described above and illustrated in the figures arepresented by way of example only and are not intended as a limitationupon the concepts and principles of the invention. As such, it will beappreciated by one having ordinary skill in the art that various changesin the elements and their configuration and arrangement are possiblewithout departing from the spirit and scope of the invention as setforth in the appended claims.

1. An electric machine comprising: a stator assembly having a statorcore and a coil supported by the stator core; a rotor assembly having ashaft and a rotor supported by the shaft for rotation with the shaftrelative to the stator core, the rotor having a first magnetic pole anda second magnetic pole, the rotor being in magnetic interaction with thestator core; and a single sensor configured to detect magneticpolarities of the rotor as the rotor rotates relative to the sensor andto generate a signal representing the detected magnetic polarities ofthe rotor, the signal being in a first state when the first magneticpole is detected and a second state when the second magnetic pole isdetected, the signal being inverted to form an inverted signal, thesignal being utilized to control current through the coil in a firstdirection when the signal is in the first state and the inverted signalbeing utilized to control current through the coil in a second directionwhen the signal is in the second state, the current through the coilresulting in an alternating magnetic field in the stator core.
 2. Anelectric machine according to claim 1, wherein the sensor is a Halleffect sensor.
 3. An electric machine according to claim 1, wherein therotor extends axially beyond the stator core in at least one direction,and wherein the sensor is positioned adjacent an axial surface of thestator core and a radial surface of the rotor.
 4. An electric machineaccording to claim 1, wherein the rotor is a permanent magnet rotor. 5.An electric machine according to claim 4, wherein the rotor includes asolid ferrite cylinder having a bore formed therein to receive at leasta portion of the shaft.
 6. An electric machine according to claim 1,wherein at least a portion of the rotor and at least a portion of theshaft are encapsulated in an encapsulation material, and wherein theencapsulation material connects the rotor to the shaft.
 7. An electricmachine according to claim 1, wherein the stator core defines a rotoropening, wherein at least a portion of the rotor is positioned in therotor opening, wherein the stator core is formed of a plurality oflaminations, and wherein each lamination is formed so the rotor openingforms a tapered air gap between at least a portion of the stator coreand a corresponding portion of the rotor.
 8. An electric machineaccording to claim 1, wherein the stator assembly includes a plasticbobbin supported by the stator core, wherein the stator core includes aC-frame portion and an I-bar portion, and wherein the coil is woundaround the plastic bobbin.
 9. An electric machine according to claim 8,wherein the I-bar portion is formed of grain-oriented electric steel.10. An electric machine according to claim 9, wherein the C-frameportion is formed of non-grain-oriented electric steel.
 11. An electricmachine according to claim 1, and further comprising a circuit board,wherein the sensor is mounted on the circuit board, and wherein thecircuit board is at least partially encapsulated such that the positionof the sensor is fixed relative to the circuit board.
 12. An electricmachine according to claim 11, wherein the rotor assembly furtherincludes first and second bearings secured to the shaft on oppositesides of the rotor, and further comprising a first bearing housing thatreceives the first bearing and a second bearing housing that receivesthe second bearing, wherein the second bearing housing includes a pocketthat receives a portion of the encapsulated sensor, and wherein thepocket locates the sensor relative to the rotor.
 13. An electric machineaccording to claim 11, wherein the sensor is entirely encapsulated. 14.An electric machine according to claim 1, wherein utilizing the signalto control current through the coil in a first direction includesutilizing the signal to control voltage applied to the coil to producecurrent through the coil in the first direction, and wherein utilizingthe inverted signal to control current through the coil in a seconddirection includes utilizing the inverted signal to control voltageapplied to the coil to produce current through the coil in the seconddirection.
 15. An electric machine comprising: a stator assembly havinga stator core and a coil assembly supported by the stator core, thestator core defining a rotor opening, the coil assembly including abobbin and a coil wound on the bobbin; a rotor assembly having a shaftand a permanent magnet rotor supported by the shaft, the rotor rotatingwith the shaft relative to the stator core, having a first magnetic poleand a second magnetic pole, being at least partially positioned in therotor opening, and being in magnetic interaction with the stator core; acontrol circuit configured to receive power from a power supply andcontrol a current through the coil, the current creating an alternatingmagnetic field in the stator core, the control circuit including asingle Hall device detecting magnetic polarities of the rotor-as therotor rotates relative to the Hall device and generating a signalrepresentative of the detected magnetic polarities of the rotor, thesignal being in a first state when the first magnetic pole is detectedand a second state when the second magnetic pole is detected, aninverter inverting the signal to generate an inverted signal, and aswitching circuit being connected to the coil and receiving an inputrepresentative of the signal and an input representative of-the invertedsignal, the input representative of the signal being utilized to controloperation of the switching circuit to allow the current through the coilin a first direction when the signal is in the first state, and theinput representative of the inverted signal being utilized to controloperation of the switching circuit to allow the current through the coilin a second direction when the signal is in the second state.
 16. Anelectric machine according to claim 15, wherein the control circuitincludes a buffer gate, and wherein the buffer gate receives an inputrepresentative of the signal and generates a buffered signal that isisolated from the signal.
 17. An electric machine according to claim 15,wherein the switching circuit includes a bridge circuit having first andsecond pairs of switching elements, each pair of switching elementshaving a conducting state and a non-conducting state, wherein the firstpair of switching elements can be in a conducting state to allow thecurrent through the coil in the first direction when the signal is inthe first state, wherein the second pair of switching elements is in anon-conducting state when the signal is in the first state, wherein thesecond pair of switching elements can be in a conducting state to allowthe current through the coil in the second direction when the signal isin the second state, and wherein the first pair of switching elements isin a non-conductive state when the signal is in the second state.
 18. Anelectric machine according to claim 17, wherein the first pair ofswitching elements are in a conducting state to allow current throughthe coil in the first direction when the signal is in the first stateunless an override condition exists, and wherein the second pair ofswitching elements are in a conducting state to allow current throughthe coil in the second direction when the signal is in the second stateunless the override condition exists.
 19. An electric machine accordingto claim 18, wherein the override condition exists when the currentthrough the coil exceeds a predetermined value.
 20. An electric machineaccording to claim 18, wherein the control circuit further includes avoltage regulator to generate a direct current rail voltage, and whereinthe override condition exists when the rail voltage is below apredetermined value.
 21. An electric machine according to claim 17,wherein the control circuit further includes a delay circuit, whereinthe delay circuit receives an input representative of the signal andgenerates a delayed signal that is delayed relative to the signal, andwherein the delayed signal is utilized to control operation of theswitching circuit such that the first and second pairs of switchingelements are prevented from each being simultaneously in a conductingstate.
 22. An electric machine according to claim 15, wherein thecontrol circuit further includes a current limit circuit that monitorsthe current through the coil in each of the first and second directionsand generates a current signal representative of a monitored currentthrough the coil, wherein the current signal is utilized to allow thecurrent through the coil when a value of the monitored current is in apredefined range and limit current through the coil when a value of themonitored current is above the predefined range.
 23. An electric machineaccording to claim 15, wherein the control circuit generates a directcurrent rail voltage, wherein the control circuit further includes avoltage detection circuit that monitors the rail voltage and generates avoltage signal representative of a monitored rail voltage, and whereinthe voltage signal is utilized to allow current through the coil when avalue of the monitored rail voltage is in a predefined range and limitcurrent through the coil when a value of the monitored rail voltage isbelow the predefined range.
 24. An electric machine according to claim15, wherein the control circuit further includes a first AND gate,wherein the first AND gate receives an input representative of thesignal and generates a first output, and wherein the first output isutilized to control operation of the switching circuit.
 25. An electricmachine according to claim 24, wherein the control circuit furtherincludes an inverter and a second AND gate, wherein the inverterreceives an input representative of the signal and generates an invertedsignal, wherein the second AND gate receives an input representative ofthe inverted signal and generates a second output, and wherein thesecond output is utilized to control operation of the switching circuit.26. An electric machine according to claim 25, wherein the controlcircuit further includes a condition monitoring circuit, wherein thecondition monitoring circuit receives an input representative of thecurrent through the coil, receives an input representative of a directcurrent rail voltage, and generates a third output, wherein the firstand second AND gates each also receive an input representative of thethird output and utilize the input representative of the third outputwhen generating the first and second outputs, respectively.
 27. Anelectric machine according to claim 26, wherein the third output is in athird state when each of the input representative of the current throughthe coil and the input representative of a direct current rail voltageare in an acceptable range, and wherein the third output is in a fourthstate when at least one of the input representative of the currentthrough the coil and the input representative of a direct current railvoltage is outside the acceptable range, and wherein the third output isutilized to limit current through the coil when the third output is inthe fourth state.
 28. An electric machine according to claim 15, whereinutilizing the input representative of the signal to control operation ofthe switching circuit to allow the current through the coil in a firstdirection includes utilizing the input representative of the signal tocontrol operation of the switching circuit to apply voltage to the coilto produce current through the coil in the first direction, and whereinutilizing the input representative of the inverted signal to controloperation of the switching circuit to allow the current through the coilin a second direction includes utilizing the input representative of theinverted signal to control operation of the switching circuit to applyvoltage to the coil to produce current through the coil in the seconddirection.
 29. An electric machine according to claim 1, wherein thestator core defines a first bore, wherein the rotor assembly furthercomprises first and second bearings secured to the shaft on oppositesides of the rotor, and wherein the electrical machine furthercomprises: a first bearing housing that receives the first bearing anddefines a second bore which aligns with the first bore; a second bearinghousing that receives the second bearing and defines a third bore whichaligns with the first and second bores; a first fastener received in thesecond, first, and third bores to secure the first and second bearinghousings to the stator assembly with the first and second bearingsreceived at least partially within the first and second bearinghousings, respectively; a circuit board; and a second fastener thatsecures the circuit board to the second bearing housing, the secondfastener being spaced from the first fastener.
 30. An electric machineaccording to claim 29, wherein the first fastener is a threadedfastener, and wherein the third bore receives an end portion of thethreaded fastener.
 31. An electric machine according to claim 29,wherein the second fastener is a push nut.
 32. An electric machineaccording to claim 29, wherein the second fastener is a threadedfastener.
 33. An electric machine according to claim 29, wherein thesecond bearing housing defines a projection, wherein the circuit boarddefines a fourth bore which aligns with the projection, and wherein thesecond fastener engages the projection to secure the circuit board tothe second bearing housing.
 34. An electric machine according to claim33, wherein a portion of the projection extends through the fourth bore,and wherein the second fastener engages the portion of the projectionthat extends through the fourth bore to secure the circuit board to thesecond bearing housing.
 35. An electric machine according to claim 33,wherein the projection is a pin cast on the second bearing bracket. 36.An electric machine according to claim 33, wherein the pin aligns withthe first, second, and third bores.
 37. An electric machine according toclaim 29, wherein the second bearing housing defines a fourth bore, andwherein the fourth bore receives an end portion of the second fastenerto secure the circuit board to the second bearing housing.
 38. Anelectric machine according to claim 37, wherein the circuit boarddefines a fifth bore which aligns with the fourth bore, and wherein thesecond fastener extends through the fifth bore to secure the circuitboard to the second bearing housing.
 39. An electric machine accordingto claim 38, wherein the fourth bore is a blind bore.
 40. An electricmachine according to claim 29, wherein the stator assembly includes aplastic bobbin supported by the stator core, wherein the stator coreincludes a C-frame portion and an I-bar portion, and wherein the coil iswound on the plastic bobbin.
 41. An electric machine according to claim29, wherein the first bore is a through bore, wherein the second bore isa through bore, and wherein the third bore is a blind bore.
 42. Anelectric machine as set forth in claim 15, wherein the stator coreincludes a C-frame portion that defines the rotor opening and an I-barportion that is formed of grain-oriented electric steel.
 43. An electricmachine according to claim 42, wherein the stator assembly includes aplastic bobbin supported by the stator core, and wherein the coil iswound on the plastic bobbin.
 44. An electric machine according to claim42, wherein the C-frame portion is formed of non-grain-oriented electricsteel.
 45. An electric machine according to claim 42, wherein the rotoris a permanent magnet rotor.
 46. An electric machine according to claim42, wherein the I-bar portion generally defines a length and a width,and wherein the length of the I-bar portion is oriented substantiallyalong the preferred magnetization direction of the grain-orientedelectric steel.
 47. An electric machine according to claim 15, whereinat least a portion of the rotor and at least a portion of the shaft areencapsulated in an encapsulation material that connects the rotor to theshaft.
 48. An electric machine according to claim 47, wherein theencapsulation material is a plastic material.
 49. An electric machineaccording to claim 47, wherein the rotor is fully encapsulated by theencapsulation material.
 50. An electric machine according to claim 47,wherein the rotor includes a solid ferrite cylinder having a bore formedtherein to receive at least a portion-o f the shaft.
 51. An electricmachine according to claim 1, wherein the stator core defines a rotoropening, and wherein the electric machine further comprises: a coilassembly supported by the stator core, the coil assembly including abobbin and a coil wound on the bobbin; first and second bearings securedto the shaft on opposite sides of the rotor; a sensor configured todetect magnetic polarities of the rotor and to generate a signalrepresenting the detected magnetic polarities of the rotor, the signalbeing utilized to control a current through the coil; a first bearinghousing that receives the first bearing; and a second bearing housingthat receives the second bearing, the second bearing housing defining apocket that receives a portion of the sensor to locate the sensorrelative to the rotor.
 52. An electric machine according to claim 51,wherein the pocket is cast in the second bearing housing.
 53. Anelectric machine according to claim 51, wherein the portion of thesensor received in the pocket is encapsulated.